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The latest version of this topic can be found at .ALLOCSTACK.

Generates a UWOP_ALLOC_SMALL or a UWOP_ALLOC_LARGE with the specified size for the current offset in the prologue.


MASM will choose the most efficient encoding for a given size.

.ALLOCSTACK allows ml64.exe users to specify how a frame function unwinds and is only allowed within the prologue, which extends from the PROC FRAME declaration to the .ENDPROLOG directive. These directives do not generate code; they only generate .xdata and .pdata. .ALLOCSTACK should be preceded by instructions that actually implement the actions to be unwound. It is a good practice to wrap both the unwind directives and the code they are meant to unwind in a macro to ensure agreement.

The size operand must be a multiple of 8.

Fore more information, see MASM for x64 (ml64.exe).

The following sample shows how to specify an unwind/exception handler:

; ml64 ex3.asm /link /entry:Example1  /SUBSYSTEM:Console  
text SEGMENT  
PUBLIC Example3  
PUBLIC Example3_UW  
Example3_UW PROC NEAR  
   ; exception/unwind handler body  
   ret 0  
Example3_UW ENDP  
Example3 PROC FRAME : Example3_UW  
   sub rsp, 16  
.allocstack 16  
   ; function body  
    add rsp, 16  
   ret 0  
Example3 ENDP  
text ENDS  

Directives Reference